A new method for excited states: Similarity transformed equation-of-motion coupled-cluster theory

et al. 2014

Recent development in particle-particle random phase approximation (pp-RPA) broadens the perspective on ground state correlation energies (van Aggelen et al. Phys. Rev. A, 88, 030501 (2013)) and N ± 2 excitation energies (Yang, et al. J.Chem. Phys.). So far Hartree-Fock and approximated density-functional orbitals have been utilized to evaluate the pp-RPA equation. In this paper, to further explore the fundamentals and the potential use of pairing matrix dependent functionals, we present the linear-response time-dependent density-functional theory with pairing elds with both adiabatic and frequency-dependent kernels. This theory is related to the density-functional theory and time-dependent density-functional theory for superconductors, but is applied to normal non-superconducting systems for our purpose. Due to the lack of the proof of the one-to-one mapping between the pairing matrix and the pairing eld for time-dependent systems, the linear-response theory is established based on the representability assumption of the pairing matrix. The linear response theory justi es the use of approximated density-functionals in the pp-RPA equation. This work sets the fundamentals for future density-functional development to enhance the description of ground state correlation energies and N ± 2 excitation energies.

“…Double-ionization-potential/double-electron-attachment equation-of-motion coupled-cluster singles and doubles (DIP/DEA-EOM-CC) 40,41 are examples of such approaches.…”

Section: Introductionmentioning

confidence: 99%

Linear-response time-dependent density-functional theory with pairing fields

Peng

Aggelen

et al. 2014

“…Such EOM-CC methods involving electron number changes have roots in Fock-Space coupled cluster (FSCC) theory [26][27][28][29][30][31][32][33] and similarity transformed EOM-CC 34,35 . A similarity among these non-N -electron-ground-state reference methods is that the N -electron ground state and excited states are constructed with the same procedure, therefore, these methods are believed have balanced treatment between the ground state and excited states.…”

Section: Introductionmentioning

confidence: 99%

Double, Rydberg and charge transfer excitations from pairing matrix fluctuation and particle-particle random phase approximation

Aggelen

2013

118

Double, Rydberg and charge transfer (CT) excitations have been great challenges for time-dependent density functional theory (TDDFT). Starting from an (N ± 2)-electron single-determinant reference, we investigate excitations for the N -electron system through the pairing matrix fluctuation, which contains information on twoelectron addition/removal processes. We adopt the particle-particle random phase approximation (pp-RPA) and the particle-particle Tamm

“…The establishment of the equivalence of pp-RPA and ladder-CCD will be beneficial to study pp-RPA properties. Furthermore, in the coupled cluster framework, the excited states based on the pp-RPA wavefunction can be strategically obtained via equationof-motion coupled-cluster [41][42][43][44] or, equivalently, linear-response coupled-cluster theory 45,46 .…”

Section: Introductionmentioning

confidence: 99%

Equivalence of particle-particle random phase approximation correlation energy and ladder-coupled-cluster doubles

Peng

Steinmann²,

Aggelen³

et al. 2013

We present an analytical proof and numerical demonstrations of the equivalence of the correlation energy from particle-particle random phase approximation (pp-RPA) and ladder-couple-cluster-doubles (ladder-CCD). These two theories reduce to the identical algebraic matrix equation and correlation energy expressions, under the assumption that the pp-RPA equation is stable. The numerical examples illustrate that the correlation energy missed by pp-RPA in comparison with couple-cluster single and double is largely canceled out when considering reaction energies. This theoretical connection will be beneficial to future pp-RPA studies based on the well established couple cluster theory.